The invention relates to a constant velocity ball joint and, more particularly, to a double-offset joint with centering means for a cage. Constant velocity ball joints include an outer joint part with an inner cylindrical guiding face provided with first, longitudinally extending ball grooves; an inner joint part with a convex guiding face provided with second, longitudinally extending ball grooves; and torque transmitting balls which run in the first and second ball grooves. The balls are held by an annular ball cage in a ball center plane E. The ball cage comprises an outer spherical control face whose greatest diameter is axially removed in a first direction by a distance x from the ball center plane E. The ball cage also comprises an inner concave control face whose greatest diameter is axially removed in a second direction by a distance x from the ball center plane E. The inner control face in the ball cage forms end stops for delimiting an axial displacement path of the inner joint part relative to the ball cage. With reference to the positions of the central planes of the control faces at the ball cage relative to the ball center plane, such joints are called double offset joints (DO joints). They are described in DE 24 61 226 C2, for example.
If the outer joint part is articulated relative to the inner joint part, the control faces at the ball cage control the balls received in circumferentially distributed cage windows in the ball cage in such a way that they move on to the plane bisecting the angle between the axes of the outer joint part and of the inner joint part. In consequence, while ignoring the different contact radii, the balls carry out a predominantly rolling movement in the outer ball grooves and in the inner ball grooves.
Because the cage, by way of the outer control face, engages the inner cylindrical guiding face of the outer joint part with a corresponding diameter, the joint is also able to carry out axial displacement movements between the outer joint part and the inner joint part. Under ideal conditions, it is assumed that by rolling movements, the balls would set themselves in the outer ball grooves and the inner ball grooves to half the axial displacement between the inner joint part and the outer joint part. In fact, however, the balls are prevented from doing so because of the substantially fitting, positive engagement between the ball cage and the inner joint part. Furthermore, because of the common axial movement of the ball cage and the inner joint part, there occurs a sliding movement between the balls and the inner ball grooves. As a result, there are generated high axial displacement forces in the joint. Moreover, any vibrations introduced into the joint are transmitted almost in their entirety.
By specifically designing the convex guiding face of the inner joint part as compared to the inner concave control face of the ball cage, it has already been proposed to permit a short axial displacement path between the ball cage and the inner joint part. This is intended to permit the required rolling movements of the balls in the inner ball grooves in a small axial region and thus to reduce friction and to tackle the problem of the transmission of vibrations in the range of slight axial vibration symptoms. But in such a case, the ball cage--because of its indifferent position and the influence of torque when the joint is articulated--moves into one of the positions of abutment relative to the inner joint part. The result is that the required effect of free rolling movements in both directions is lost. In addition, if the joint is used in the motor vehicles for example, vibrations are transmitted "rigidly" from the engine-gearbox unit via the joint to the vehicle body.